The present invention relates to waste water treatment equipment and waste water treatment method capable of concurrently treating an exhaust gas containing fluorine and organic matter when treating a waste water that contains fluorine and organic matter or contains fluorine, organic matter and hydrogen peroxide.
Conventionally, the waste water that contains fluorine and organic matter or contains fluorine, organic matter and hydrogen peroxide discharged from various kinds of industrial facilities, semiconductor plants and so on (the water referred to as waste water hereinafter) has generally been treated separately by waste water treatment equipment and exhaust gas treatment equipment.
That is, with regard to the fluorine in the waste. water, slightly-soluble calcium fluoride is generated principally by incorporating a large amount of slaked lime into the waste water and is precipitated for the removal of the fluorine. The organic matter such as a surfactant and an organic solvent in the waste water have been treated after the treatment of fluorine by performing biological treatment with a nutrition put in a treatment water tank different from that of the treatment of fluorine or by means of an activated carbon adsorption in a case where the organic matter concentration is low.
On the other hand, the fluorine in the exhaust gas has been treated by exhaust gas treatment equipment represented by an acid scrubber, while the organic matter such as the organic solvent in the exhaust gas has been treated by exhaust gas treatment equipment (specifically, an activated carbon adsorption filter unit) stowed with activated carbon. As a representative of the organic matter in the exhaust gas, there can be enumerated organic solvent such as acetone and isopropyl alcohol. Then, the organic solvent is generally treated by adsorption with the activated carbon adsorption unit.
Generally in the activated carbon adsorption filter unit, there are provided two or more activated carbon filters, which alternately repeat adsorption and desorption to continuously treat the organic solvent by adsorption. However, the activated carbon adsorption filter unit does not decompose the organic solvent itself, and therefore, the total amount of the organic solvent itself does not vary.
Furthermore, the existing semiconductor plants and liquid crystal plants are frequently subjected to redevelopment by facility renewal, and there is frequently occurring the phenomenon that the originally planned capability of the exhaust gas treatment equipment becomes insufficient. The reason of the insufficiency of the exhaust gas treatment equipment capability is that the greater number of production units than originally planned tend to be installed and the flow rate of the exhaust gas to be treated in using the production units increases with the introduction of a new production unit.
In contrast to this, the prior art exhaust gas treatment equipment is hard to increase its treatment capability by modifying the aforementioned units after being once installed. Therefore, in order to improve the exhaust gas treatment capability, it is required to newly install additional exhaust gas treatment equipment.
However, newly installing the additional exhaust gas treatment equipment is often difficult in terms of plan from the viewpoint of the initial cost and space.
Therefore, the insufficiency of the exhaust gas treatment capability has hindered the smooth renewal of the production facilities in the semiconductor plants and the liquid crystal plants.
On the other hand, in regard to the influence on the waste water treatment equipment, with the current trend toward the removal of Fleon, in particular, cleaning methods by combinations of a variety of surfactants, acetone, alcohol and so on instead of Fleon for cleaning use in the semiconductor plants and liquid crystal plants are expected as important cleaning methods for the total abolition of Fleon, judging from the their good cleaning performances and small damages on components.
However, the implementation of the cleaning method by a combination of ultrapure water and a surfactant or a variety of acids has the problem that calcium fluoride waste extremely increases with respect to, in particular, the fluorine treatment in the above plants and the problem that the remaining surfactant influences the water quality of the treated water.
Furthermore, the surfactant, which sometimes have a sterilizing effect on the microorganisms utilized for waste water treatment, makes it difficult to perform microorganic treatment.
In view of the aforementioned problems of the prior art waste water treatment technique, there is proposed improved treatment equipment and treatment method as shown, in FIG. 13 (refer to the prior art reference of Japanese Patent Laid-Open Publication No. HEI 8-57498) for concurrently treating a waste water containing fluorine and organic matter and an exhaust gas containing fluorine and organic matter.
In FIG. 13, the reference numeral 101 denotes a first reaction equalizing tank. A first lower section 101a of this first reaction equalizing tank 101 is stowed with calcium carbonate mineral 109A stowed in a stowing basket 110A. The first reaction equalizing tank 101 has a blower 117, a pipe 120A extending from this blower 117 and a diffuser pipe 111A provided at the end of this pipe 120A. The diffuser pipe 111A is arranged at the bottom of the first lower section 101a of the first reaction equalizing tank 101 while constituting an aerating means.
The waste water that contains fluorine and organic matter and is discharged from the production process is first introduced into the first reaction equalizing tank 101.
The water level of the waste water inside the first reaction equalizing tank 101 is adjusted so that the calcium carbonate mineral 109A is submerged. The waste water is strongly stirred by the aerating means. Due to this stirring, the fluorine ion in the waste water and calcium ion dissolving from the calcium carbonate mineral 109A react each other with the lapse of time. In this case, acids such as hydrofluoric acid and sulfuric acid are mixed in the waste water, so that the waste water exhibits acidity. Therefore, calcium tends to easily dissolve from the calcium carbonate mineral 109A. Accordingly, crystalline calcium fluoride (crystal seed) is easily generated.
In a first upper section 101b of the first reaction equalizing tank 101 is arranged a first reaction water sprinkling section 103 stowed with the calcium carbonate mineral 109A and a plastic filler 113A.
Then, in a space S1 leading the exhaust gas and being located below the first reaction water sprinkling section 103 is provided a duct 129 that communicates with this space S1 and is projecting sideways. The end of this duct 129 is mounted with a ventilation fan 112, and this ventilation fan 112 allows the exhaust gas containing fluorine and organic matter from the plant to be led into the space S1.
In a lowermost portion of the first reaction water sprinkling section 103 is provided a grid plate 115A. As shown in FIG. 13, this grid plate 115A has its grid extending in the vertical direction, so that the projected area in the vertical direction is made much smaller than the projected area in the lateral direction. Therefore, the exhaust gas from the duct 129 can easily pass through the grid plate 115A and reach the first reaction water sprinkling section 103.
Then, the exhaust gas whose fluorine has been treated while passing through the first reaction water sprinkling section 103 from the lower side to the upper side, i.e., the treated gas is introduced into an exhaust gas introducing space S2 below a second reaction water sprinkling section 104 provided in a second upper section 102b of a second reaction equalizing tank 102 by way of a duct 121 connected to the uppermost portion of the first reaction equalizing tank 101.
The second reaction equalizing tank 102 is stowed with a calcium carbonate mineral 109B and a charcoal 123 as a filler. Then, at the bottom of the second reaction equalizing tank 102 is arranged a diffuser pipe 111B for pneumatically stirring the inside of the tank. A bottom surface 102c of the second reaction equalizing tank 102 is inclined toward a lower end 116b where an air lift pump 116B has an inlet so that the generated calcium fluoride crystal (crystal seed) can be easily introduced into the second reaction water sprinkling section 104 by an air lift pump 116B.
The calcium carbonate mineral 109B and the charcoal 123 stowed in this second reaction equalizing tank 102 are the microorganism fixing carrier for microorganism, and with the lapse of time, a biofilm is formed on the surfaces of the calcium carbonate mineral 109B and the charcoal 123. If an excessive sludge, i.e., an active sludge generated from another biotic treatment site is put into the second reaction equalizing tank 102, then the biofilm can be speedily made to adhere to the microorganism fixing carrier. Then, the organic matter in the waste water is treated by the microorganism of the biofilm generated on the surfaces of the calcium carbonate mineral 109B and the charcoal 123 in the second reaction equalizing tank 102.
As described above, the fluorine in the waste water is treated by being circulated through the first reaction equalizing tank 101 stowed mainly with the calcium carbonate mineral, not with a large amount of slaked lime, reacted with the calcium carbonate mineral 109A to become a crystalline calcium fluoride, made to pass through the second reaction equalizing tank 102, condensed in a condensation tank 105 and precipitated in a sedimentation tank 106. The organic matter such as an organic solvent and a surfactant in the waste water is treated mainly by the microorganism fixed on the calcium carbonate and the charcoal in the second reaction equalizing tank 102.
On the other hand, the exhaust gas treatment section is provided in the upper sections of the first reaction equalizing tank and the second reaction equalizing tank, and the fluorine and organic matter in the exhaust gas are dissolved in the circulating waste water and treated by reaction with the calcium carbonate mineral inside the reaction equalizing tank and the microorganism. That is, the treatment units of the waste water and exhaust gas are integrated with each other, thereby effectively utilizing the installation area. It is to be noted that the reference numeral 107 denotes a sludge concentrating tank and the reference numeral 108 denotes a filter press in the figure.
The example shown in FIG. 13, which is a compact treatment unit for efficiently treating the fluorine and organic matter discharged from the semiconductor plant or the liquid crystal plant, has the problems i), ii) and iii) with regard to the waste water treatment and the problems iv) and v) with regard to the exhaust gas treatment as follows.
i) In order to allow the waste water to flow between the stowed calcium carbonate mineral pieces, there is selected calcium carbonate mineral having a relatively large diameter of 2 to 7 cm, and the mineral is used entirely in a fixed state. Therefore, calcium fluoride generated as a consequence of the reaction of the fluorine in the waste water with calcium remains between the calcium carbonate mineral pieces in the fixed state and becomes a, mass after a long-time operation. Then, the mass gradually increases to spread throughout the tank, and this leads to a reduced contact between the waste water and the calcium carbonate mineral, resulting in reduced treatment efficiency.
ii) The treatment unit has a height of up to several meters on the plant scale, and the replenishment inlet of the calcium carbonate mineral is located in a high position above the center portion, and therefore, the tank is hard to be automatically replenished with the calcium carbonate mineral having a size of a diameter of 2 to 7 cm.
iii) The calcium carbonate mineral is relatively inexpensive. However, the material pieces having a size of a diameter of 2 to 7 cm are availed less on the market, and it is to inevitably be a custom-made article, resulting in a high cost.
iv) As the filler in the upper section of the first reaction tank, there has been stowed calcium carbonate mineral having a diameter of 5 to 7 cm. Therefore, the filler has an air resistance and a small amount of treatment air flow rate in comparison with the equipment scale. Furthermore, as the filler in the upper section of the second reaction tank, there has been stowed charcoal having a diameter of 5 to 7 cm. Therefore, the filler also has an air resistance and a small amount of treatment air flow rate in comparison with the equipment scale.
v) The crystalline calcium fluoride (crystal seed) has an insufficient surface area and an insufficient exhaust gas treatment capability.